An object of a test of an over the air (OTA) technology of the MIMO antenna is to guarantee that test results from labs can really reflect wireless performances of a wireless terminal in a variety of complex and practical environments and in use states.
The main MIMO wireless terminal test methods provided by 3rd Generation Partnership Project (3GPP), an international wireless standard organization, include a multi-probe anechoic chamber (MPAC) method, a radiated two-stage (RTS) method and a reverberation chamber method. Specifically, the RTS method is based on a conducted two-stage method but not involving conducting wires. With the RTS method, a signal is transmitted to a device under test (DUT) in free space simulated by an anechoic chamber, and an inverse matrix of a space propagation matrix is demodulated with a corresponding method. In such a manner, two virtual conducting wires may be achieved in the space and the signal may be transmitted to a receiver via the virtual conducting wires.
In order to make the RTS method more readily appreciated, the RTS method of the MIMO wireless terminal test is introduced briefly below with reference to FIG. 1, which is a schematic diagram of an RTS method in the related art, and a test process thereof mainly includes the following steps:
step A, obtaining antenna pattern information of a plurality of antennas of a MIMO wireless terminal (i.e., a DUT), in which the antenna pattern information contains gain information in a plurality of directions of each antenna and phase shift information of any two antennas receiving the same signal in a plurality of directions, and the like;
step B, simulating a complete MIMO transmission channel by fusing the antenna pattern information of the plurality of antennas of the DUT obtained and a preset MIMO channel propagation model so as to further generate a throughput testing signal;
step C, determining a calibration matrix for the DUT in an anechoic chamber according to relative positions and directions of the DUT to a testing antenna in the anechoic chamber, and generating a transmitting signal for test according to the calibration matrix and the throughput testing signal obtained; and
step D, feeding the transmitting signal for test into a plurality of testing antennas of the electromagnetic anechoic chamber and transmitting the transmitting signal to the MIMO wireless terminal through the testing antennas so as to test the wireless terminal.
In step C, the transmitting signal for test is generated according to the calibration matrix, and the calibration matrix herein reflects an amplitude shift and a phase shift in a signal transmission from the testing antenna to the receiving antenna of the MIMO wireless terminal. Since not all the calibration matrixes have an inverse matrix, different calibration matrixes needs to be achieved by changing the relative position and/or orientation between the DUT and the testing antenna of the MIMO system. Furthermore, in the related art, for any of the calibration matrixes with a certain relative position and/or orientation between the DUT and the testing antenna, an isolation degree of the MIMO system needs to be measured. Subsequently, a matrix having a maximum isolation degree is selected for generating the transmitting signal for test.
With such method for measuring the isolation degree in the related art, a lot of time needs to be spent since there may be a plurality of relative position and/or orientation between the DUT and the testing antenna, particularly in a case of high-order calibration matrixes. Moreover, efficiency for solving the isolation degree is low due to human intervention in the testing process, as it needs a tester to subjectively determine whether the isolation degree meets requirements or not. Because of the low efficiency for solving the isolation degree in the related art, a long time is needed in determining a space propagation matrix according to the isolation degree, and further in generating the transmitting signal for test according to the space propagation matrix determined, thus negatively affecting an efficiency for generating the transmitting signal for test seriously and resulting in a low testing efficiency.